At present, the materials used for making bearing cages do not give entire satisfaction, in particular in cryogenic conditions, and they also suffer from numerous drawbacks associated firstly with mechanical problems that arise at high speeds of rotation and that cause the cage to break, and secondly with the friction between the cage and the balls, rollers, or needles it contains and which are of a kind that can give rise to overheating of the bearing.
A partial solution to these difficulties is provided at present by using composite materials based on glass fiber and on PTFE which are capable, in particular, of operating at high speeds of rotation and which are manufactured mainly on the basis of two conventional methods, namely injection and winding.
The first method suffers from the major drawback of not enabling good mechanical characteristics to be obtained, but it has the advantage of making it easier to add any kind of additive suitable for imparting specific properties to the material made by the method.
The second method which consists in applying a thread to a mandrel that is rotating makes it possible to obtain mechanical characteristics which are good in a circumferential direction because the fibers are oriented, but which are nevertheless poor in a longitudinal direction, thereby having the consequence of limiting the traction strength of bearings made by this method. The weakness of this type of winding persists even when the threads are crossed (using the principle of helical winding) at an optimum angle close to 50.degree.. In addition, the materials obtained by this method suffer from a highly random coefficient of friction that depends, in particular, on the winding directions of the various fibers and that affects both the lifetime and the stability of cages or bearings made with this material. It is also appropriate to observe that the presence of glass fibers imparts abrasive properties to this material which can give rise to certain drawbacks.
Although this simple method of winding applied to sheets of fabric makes it possible to obtain mechanical characteristics that are good in both axial and circumferential directions, it does not enable adequate tribological characteristics of friction and wear resistance to be obtained since it prevents lubricants, are not "impregnatable", being included in significant volume.